How do I play Left 4 Dead on Xbox Live with other people?

ok,this is too easy but i ll help u!First of all,login to steam,if u havent a account make a new one.Then,choose in the main game menu 'campaign' or 'versus' etc and then choose 'online play'(or something like that),then u can see some lobbys(campaigns who arent full of players),just choose one and join the game!U can also make a new lobby and other players will join ur lobby!